[Hassam]

The default MT4 Bollinger Bands indicator does not have as option for using a EMA instead of a SMA. I have coded a custom Bollinger Bands indicator that has the EMA option. Below is a screenshot of the Bollinger Bands with EMA. I have chosen 2 standard deviation with EMA 21.



If you want the MQL4 code for the custom Bollinger Bands with EMA option as well as the SMA option, you can copy that too from below:

Code:

//+------------------------------------------------------------------+
//|                                                       BB_EMA.mq4 |
//|                                                     Ahmad Hassam |
//|                                      https://www.doubledoji.com/ |
//+------------------------------------------------------------------+
#property copyright "Ahmad Hassam"
#property link      "https://www.doubledoji.com/"
#property version   "1.00"
#property strict
#property indicator_chart_window
#property indicator_buffers 3
#property indicator_color1 Red
#property indicator_color2 DeepSkyBlue
#property indicator_color3 DeepSkyBlue



// External parameters
//choose the number of bars to use
input int BandsPeriod = 21; //Smoothing Period
input int BandsShift = 0;   //Shift
//---choose which averaging method to use
input ENUM_MA_METHOD BandsMethod = MODE_EMA;  //Smoothing Methods
//---choose which price to use
input ENUM_APPLIED_PRICE priceBB = PRICE_CLOSE; //Applied Price

//---choose the number of standard deviations to use
input int Deviations = 2; // No Of Standard Deviations
extern int K=20; // Standard Deviation Lookback
double StdDev=0.0;
//---- buffers
double EMA[];
double upperBand[];
double lowerBand[];

//+------------------------------------------------------------------+
//| Custom indicator initialization function |
//+------------------------------------------------------------------+
int init()
{
//---- indicators
SetIndexStyle(0,DRAW_LINE);
SetIndexBuffer(0,EMA);
SetIndexLabel(0,"EMA");
SetIndexStyle(1,DRAW_LINE);
SetIndexBuffer(1,upperBand);
SetIndexLabel(1,"UpperBand");
SetIndexStyle(2,DRAW_LINE);
SetIndexBuffer(2,lowerBand);
SetIndexLabel(2,"LowerBand");
//----

return(0);
}

//+------------------------------------------------------------------+
//| Custom Bollinger Bands Indicator                              |
//+------------------------------------------------------------------+

// start() function
  int start()
 {
 int Count=0;
 int limit=0;
 int counted_bars=IndicatorCounted();
 int CalculateBars = Bars - counted_bars;
//  double StdDev;

/*
  calculate the moving average
  double  iMA(
  string       symbol,           // symbol
  int          timeframe,        // timeframe
  int          ma_period,        // MA averaging period
  int          ma_shift,         // MA shift
  int          ma_method,        // averaging method
  int          applied_price,    // applied price
  int          shift             // shift
  );
 
calculate the standard deviation  
  double  iStdDev(
  string       symbol,           // symbol
  int          timeframe,        // timeframe
  int          ma_period,        // MA averaging period
  int          ma_shift,         // MA shift
  int          ma_method,        // MA averaging method
  int          applied_price,    // applied price
  int          shift             // shift
  );
*/
// NULL means current chart symbol
// 0 means current chart timeframe
if (counted_bars==0)
     {
     limit=Bars-1;
     
     }
  if (counted_bars>0)
     {
     limit=CalculateBars-1;
     
     }

for(Count = limit-40; Count >= 0; Count--)
{
        EMA[Count] = iMA(NULL,0,BandsPeriod,BandsShift,BandsMethod,priceBB,Count);
        StdDev = iStdDev(NULL,0,BandsPeriod,BandsShift,BandsMethod,priceBB,Count);
        upperBand[Count] = EMA[Count] + (StdDev * Deviations);
        lowerBand[Count] = EMA[Count] - (StdDev * Deviations);
       
       
}
//----
  return(0);
 }
//+------------------------------------------------------------------+

[Hassam]

This is a slight modification of the standard Bollinger Bands indicator. Instead of calculating the standard deviation of closing price, I have calculated the standard deviation of log returns of closing price and plotted as two bands with mean as EMA. The standard deviation bands are 3 standard deviations away from the EMA. Below is a screenshot of this new indicator!



If you want to the MQL4 code, below I have posted the MQL4 code as well.

Code:

//+------------------------------------------------------------------+
//|                                                   ModifiedBB.mq4 |
//|                                                     Ahmad Hassam |
//|                                      https://www.doubledoji.com/ |
//+------------------------------------------------------------------+
#property copyright "Ahmad Hassam"
#property link      "https://www.doubledoji.com/"
#property version   "1.00"
#property strict
#property indicator_chart_window
#property indicator_buffers 3
#property indicator_color1 Red
#property indicator_color2 DeepSkyBlue
#property indicator_color3 DeepSkyBlue


#include <General1.mqh>
// External parameters
//choose the number of bars to use
input int BandsPeriod = 21; //Smoothing Period
input int BandsShift = 0;   //Shift
//---choose which averaging method to use
input ENUM_MA_METHOD BandsMethod = MODE_EMA;  //Smoothing Methods
//---choose which price to use
input ENUM_APPLIED_PRICE priceBB = PRICE_CLOSE; //Applied Price

//---choose the number of standard deviations to use
input int Deviations = 3; // No Of Standard Deviations
extern int K=40; // Standard Deviation Lookback
//---- buffers
double EMA[];
double upperBand[];
double lowerBand[];
double logReturn[];
double std[];



//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit()
 {
//custom indicator buffers mapping
IndicatorBuffers(3);
 
//---- indicators
SetIndexStyle(0,DRAW_LINE);
SetIndexBuffer(0,EMA);
SetIndexLabel(0,"EMA");
SetIndexStyle(1,DRAW_LINE);
SetIndexBuffer(1,upperBand);
SetIndexLabel(1,"UpperBand");
SetIndexStyle(2,DRAW_LINE);
SetIndexBuffer(2,lowerBand);
SetIndexLabel(2,"LowerBand");
//----
ArraySetAsSeries(EMA,true);
ArraySetAsSeries(upperBand,true);
ArraySetAsSeries(lowerBand,true);
ArraySetAsSeries(std,true);
ArrayResize(std,Bars);
ArraySetAsSeries(logReturn,true);
ArrayResize(logReturn,Bars);


     
//---
  return(INIT_SUCCEEDED);
 }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int OnCalculate (const int rates_total,      // size of input time series
                const int prev_calculated,  // bars handled in previous call
                const datetime& time[],     // Time
                const double& open[],       // Open
                const double& high[],       // High
                const double& low[],        // Low
                const double& close[],      // Close
                const long& tick_volume[],  // Tick Volume
                const long& volume[],       // Real Volume
                const int& spread[] )        // Spread
 
 
 {      
     
     int bars1 = rates_total - 2;
     if (prev_calculated > 0) bars1 =  rates_total - (prev_calculated - 1);
     for ( int i =  bars1; i >= 0; i--)
     {
     
        EMA[i] = iMA(NULL,0,BandsPeriod,BandsShift,BandsMethod,priceBB,i);
        logReturn[i] = MathLog(Close[i])- MathLog(Close[i+1]);
       
     
     }
     int bars2 = rates_total - K - 1;
     if (prev_calculated > 0) bars2 =  rates_total - (prev_calculated - 1);
     for ( int i =  bars2; i >= 0; i--)
     {
     
        std[i]=standardDeviation(logReturn,K,i);
        upperBand[i] = EMA[i]*(1 + (std[i]*Deviations));
        lowerBand[i] = EMA[i]*(1- (std[i]*Deviations));
     
     }
     
     
     return(rates_total);
 }
//+------------------------------------------------------------------+